Two-cycle engine with electronic fuel injection

ABSTRACT

A fuel injection system for a two-stroke cycle engine comprising an air manifold; a throttle valve; a fuel injector; a fuel supply system including a fuel pump; a battery voltage sensor; an air temperature sensor; an engine speed sensor; a timing sensor; a barometric pressure sensor; a throttle position sensor; a first data processor for receiving and processing sensing signals for determining fuel injector duration and timing and fuel pump operating speed; a first data processor temperature sensor for sensing the relative temperature of certain electronic components in the first data processor; a heater operatively associated with the first data processor electronic components for selectively heating the electronic components; and a second data processor operable independently of the first data processor for receiving an electronic component temperature sensing signal and for generating a control signal to the heater responsive thereto for heating the components when the temperature thereof is below a predetermined minimum value.

The present application is a continuation of U.S. patent applicationSer. No. 119,626 filed Nov. 12, 1987.

BACKGROUND OF THE INVENTION

The present invention relates generally to two-stroke operating cycleengines and, more particularly, to a two-stroke engine fuel injectionsystem and control system therefor which are adapted for extreme weatherconditions.

Two-stroke operating cycle engines (two-cycle engines), although lessfuel-efficient than four-stroke operating cycle engines (four-cycleengines), are capable of developing greater horsepower and torque than acomparably-sized four-cycle engine. This feature has led to the use oftwo-cycle engines in many environments in which operating efficiency issecondary to torque and weight considerations.

Electronically-controlled fuel injection is widely used in four-cycleengines. In electronic fuel injection used in four-cycle engines, sensorreadings associated with various engine operating parameters are used tocalculate an optimum fuel/air mixture for the engine. Fuel is theninjected directly into the engine's cylinders in the proper amount basedupon this electronically determined fuel/air mixture. In some four-cycleengine fuel injection systems, the fuel is injected into an air plenumupstream of the cylinder and is subsequently allowed to enter thecylinder with the plenum air through operation of an intake valve.Electronic fuel injection systems have replaced conventional carburetorsin many four-cycle engines, especially in the automotive industry.However, fuel injection is not in general use with two-cycle engines andhas not heretofore been used with small-displacement two-cycle engineswhich are used under severe cold weather conditions, for a number ofreasons. Small two-cycle engines are used in association with equipmentthat is relatively inexpensive as compared to automobiles and othermachines with which electronic fuel injection has been widely used inthe past. In relatively large, expensive machinery, the cost associatedwith modifying basic engine components to enable internal mounting ofvarious engine parameter sensors may be justified by increased fuelsavings and engine performance and may amount to a relatively smallportion of the purchase price of such an automobile, etc. In smallerengine environments, the cost of internal engine modification toexisting engine assemblies would, in most cases, far outweigh any fuelsavings which might be achieved by an electronic fuel injection unit andwould represent a substantial increase in the cost of the associatedsmall machine, e.g. snowmobile, dirt bike, etc., powered by thetwo-cycle engine.

Fuel injection systems without electronic controls have been used ontwo-cycle engines, but have not been satisfactory on small-displacement,small-mass two-cycle engines. The reason that fuel injection withoutelectronic control has not been used successfully in small two-cycleengines is that such engines lack flywheels and other high-mass rotatingcomponents which tend to stabilize engine operation. Dueto this lack ofa large rotating mass in such engines, even a short duration mismatchbetween the rate at which fuel is actually delivered to the engine andthe optimum engine fuel rate requirements will cause engine sputter orrapid deceleration and stalling. Small, two-cycle engines are especiallysubject to malfunction under variable operating conditions such aschanges in sea level, with associated barometric changes and changes inambient air temperature. Many machines such as snowmobiles, snowblowers,dirt bikes, etc., are operated in such widely variable operatingconditions. In view of the costs associated with engine modification forsensors' need for electronic control of fuel injectors and in view ofthe fact that the engine parameters which are critical to control offuel injectors for two-cycle engines were not, prior to the presentinvention, understood in the art, a successful electronically-controlledfuel injection system for small, two-cycle engines which are subject toextremes in operating conditions has not been developed in the priorart.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide an electronic fuelinjection system for a two-cycle engine which requires no internalmodification to the basic engine assembly.

It is another object of the present invention to provide an electronicfuel injection control system which may be readily adapted for use withany conventional two-stroke cycle engine assembly.

It is another object of the present invention to provide a relativelysmall two-stroke cycle engine with electronic fuel injection which iscapable of operation under variable and extreme conditions of airtemperature and under widely varying barometric pressure conditions.

It is another object of the present invention to provide a fuelinjection system for a two-cycle engine in which fuel injection takesplace in an air manifold.

It is another object of the present invention to provide a fuelinjection and control system for a two-cycle engine in which all fuelinjectors simultaneously inject fuel into portions of an air manifoldwhich are associated with individual cylinder/crankcases.

It is another object of the present invention to provide a controlsystem for a electronic fuel injection system which utilizes relativelyinexpensive electronic components and which is not subject to electroniccomponent malfunction associated with low-temperature operation.

It is another object of the present invention to provide an electronicfuel injection system for a two-cycle engine which includes anelectronically-stored fuel map indicative of the optimum fuelrequirements for the engine under standard operating conditions overvariable engine speed conditions and variable throttle conditions.

It is another object of the present invention to provide an electronicfuel injection system which provides a selected set of operatingcondition sensor inputs which do not require internal engine unitmodifications and which provide optimized engine performance.

SUMMARY OF THE INVENTION

The present invention is directed to an electronic fuel injection systemfor a small two-cycle engine. One aspect of the invention is atemperature control assembly which is operably associated with anelectronic central processing unit of the type having electroniccomponents which are subject to malfunction under low temperatureconditions. The electronic components of the heating assembly are notsubject to malfunction under low temperature conditions and are designedto produce a heating response which is inversely proportional totemperature below a predetermined threshold temperature. The heatingassembly is preferably mounted within a relatively small enclosure whichalso houses the electronic control system central processing unit. Theheating assembly senses the temperature within the relatively smallenclosure and rapidly heats electronic components within the relativelysmall enclosure to a predetermined temperature in response to sensing anenvironmental temperature within the enclosure which is below thepredetermined temperature. The heating system may be actuated at thesame time the electronic control system is actuated such as by theturning of the ignition switch of an associated machine, such as asnowmobile, etc.

Another feature of the present invention is th provision of anelectronically-controlled fuel injection system which has a plurality ofsensor inputs which are limited to the sensor inputs which are criticalto the operation of a two-cycle engine and which may be mountedexternally of a main engine assembly comprising a cylinder crankcase,piston, and crankshaft exclusive of the carburetion/fuel injectionsystem therefor. The electronically-controlled fuel injection system ofthe present invention may thus be used without modification of existingtwo-cycle engine assemblies and is controlled by a CPU which may includea programmable memory device such as an EPROM which may be selectivelyprogrammed for any particular engine assembly with which the electronicfuel injection system is to be used. Another feature of the invention isthe injection of fuel from a fuel injector into a portion of an airmanifold which is in direct fluid communication with the crankcaseportion of each individual cylinder/crankcase assembly. This injectionof fuel into a manifold upstream of a crankcase provides mixing of aprecise amount of fuel and air prior to entry of fuel into the crankcaseand also enables all fuel injectors to be opened and closedsimultaneously, rather than being timed to the operation of eachassociated piston.

Thus, the present invention may comprise a control system forcontrolling the operation of a machine designed to be operated in arelatively broad air temperature, comprising: (a) at least oneperformance variable sensing means for sensing the present state of apreselected variable associated with machine performance and forgenerating a performance variable sensing signal indicative of saidpresent state of said preselected performance variable; (b) a first dataprocessing means for receiving and processing said performance variablesensing signal and for generating a control signal based upon theprocessing of said sensing signal for controlling at least one operatingparameter of said machine; said data processing means comprising atleast one temperature-sensitive electronic circuit component which issubject to malfunction below a predetermined malfunction temperaturewhich is within said relatively broad operating temperature range ofsaid machine; (c) component environment temperature sensing means forsensing the temperature within the immediate operating environment ofsaid temperature-sensitive electronic circuit component and forgenerating a temperature signal representative of the sensedtemperature; (d) a second data processing means which operatesindependently of said first data processing means and which is notsubject to temperature-related malfunction within said operatingtemperature range of s id machine for processing said signal from saidcomponent environment temperature sensing means and generating a heatingcontrol signal responsive thereto when the temperature in saidelectronic circuit environment is sensed to be below said predeterminedmalfunction temperature; (e) heating means responsive to said heatingcontrol signal for heating said temperature sensitive electroniccomponent environment in response to said control signal; (f) powersupply means for providing electric energy for operating said controlsystem; (g) switch means for selectively operably electricallyconnecting or disconnecting said energy supply means and electricallyoperated components of said control system.

The present invention may also comprise a fuel injection system for atwo-stroke cycle engine of the type comprising at least one cylinder, acrankcase associated with said cylinder, a piston reciprocally mountedin said cylinder and crankcase; a reciprocally openable and closablecrankcase inlet for enabling combustible fluid to be drawn into thecrankcase, a reciprocally openable and closable transfer port fortransferring combustible fluid compressed in said crankcase to saidcylinder, an ignition system for igniting compressed combustible fluidin said cylinder, a reciprocally openable and closable exhaust port insaid cylinder for enabling exhaust of burned combustible fluid from saidcylinder, a crankshaft connected to said piston for transferringmechanical energy from said piston to a drive unit, and an electricalenergy supply source including a battery for operating the ignitionsystem and other electrical components, comprising: (a) air manifoldmeans operably associated with said crankcase inlet; (b) throttle valvemeans operably positioned in said air manifold means for controllingairflow into said crankcase inlet, said throttle valve means dividingsaid manifold means into an upstream portion positioned remote from saidcrankcase inlet and a downstream portion positioned contiguously withsaid crankcase inlet; (c) fuel injection means for injecting a finespray of fuel into said downstream portion of said manifold meanswhereby a mixture of air and fuel is provided in said downstream portionof said manifold means which is subsequently drawn into said crankcasethrough said crankcase inlet; (d) fuel supply means for supplying fuelto said fuel injection means comprising: (i) fuel reservoir means forholding a volume of fuel therein and having a reservoir inlet and areservoir outlet; (ii) fuel circulation conduit means for transferringfuel from said fuel reservoir to said fuel injection means comprising afirst end inlet in fluid communication with said fuel reservoir outlet,a second end outlet in fluid communication with said fuel reservoirinlet and an intermediately positioned fuel injection outlet positionedin fluid communication with said fuel injection means; (iii) fuel pumpmeans operatively associated with circulation conduit means at aposition thereon between said conduit means first end inlet and saidconduit means fuel injector outlet for pumping fuel through saidcirculating conduit; (iv) pressure limiting regulator means operativelyassociated with said circulation conduit means at a position thereonbetween said conduit means fuel injector outlet and said conduit meanssecond end outlet for preventing pressure in said conduit means fromexceeding a predetermined maximum pressure; (e) battery voltage sensingmeans for sensing battery voltage and for providing a battery voltagesensing signal representative thereof; (f) air temperature sensing meansfor sensing the temperature of air in said upstream portion of saidmanifold means and for providing an air temperature signalrepresentative thereof; (g) engine speed sensing means for sensing thespeed of revolution of said engine and for providing an engine speedsignal representative thereof; (h) timing sensing means for sensing eachoccurrence of a predetermined cyclically repeating state of said engineand for providing a timing signal indicative thereof; (i) barometricpressure sensing means for sensing atmospheric air pressure and forgenerating a barometric pressure sensing signal representative thereof;(j) throttle position sensing means for sensing the relative amount ofopening of said throttle valve means and for generating a throttleposition signal representative thereof; (k) first data processing meansfor receiving and processing said sensing signals comprising: (i) meansfor processing said engine speed sensing signal and said throttleposition sensing signal and for generating a priming control signal tosaid fuel injection means for selectively injecting or not injectingfuel into said manifold means based on said engine speed signal and saidthrottle position signal; (ii) means for receiving and processing saidengine speed signal and throttle position signal for determining a basefuel injection value; (iii) means for receiving and processing said airtemperature signal and calculating an air temperature modification valueof said base fuel injection value; (iv) means for receiving andprocessing said barometric pressure sensing signal for calculating abarometric pressure modification value of said base fuel injectionvalue; (v) means for receiving and processing said engine temperaturesignal for calculating an engine temperature modification value of saidbase fuel injection value; (vi) means for determining a total fuelinjection value representative of the total fuel amount which is to beinjected by said fuel injection means during a single two-strokeoperating cycle of said piston from said base fuel injection value, saidair temperature modification value, said barometric pressuremodification value, and said engine temperature modification value;(vii) means for determining an injector open duration interval based onsaid total fuel injection value and a known fuel output rate capacity ofsaid fuel injection means; (viii) means for generating a control signalfor opening said injection means for said determined injector durationopen interval at a predetermined point in time determined from saidtiming sensing signal; (ix) means for receiving and processing saidengine speed signal for overridingly terminating fuel injection meansoperation in response to an engine speed sensing signal indicative of apredetermined maximum speed and for restoring fuel injection meansoperation in response to an engine speed sensing signal indicative of apredetermined restore operation speed lower than said predeterminedmaximum speed; (x) means for receiving and processing said engine speedsensing signal and for generating a pump control signal in responsethereto for maintaining said pump at an optimum operating speed forproviding said predetermined maximum operating pressure in said fuelcirculation conduit means at said pump; (l) first data processing meanstemperature sensing means for sensing the relative temperature ofcertain electronic components in said first data processing means andproviding a component temperature sensing signal indicative thereof; (m)heating means operative associated with said first data processing meanselectronic components for selectively heating said electroniccomponents; (n) second data processing means operable independently ofsaid first data processing means for receiving said electronic componenttemperature sensing signal and for generating a control signal to saidheating means responsive to said component temperature sensing signalfor heating said components when the temperature thereof is below apredetermined minimum value.

BRIEF DESCRIPTION OF THE DRAWING

An illustrative and presently preferred embodiment of the invention isshown in the accompanying drawing in which:

FIG. 1 is a schematic illustration of a two-stroke cycle engine withelectronically-controlled fuel injection.

FIG. 1A is a schematic illustration of the engine of FIG. 1 showingadditional cylinder portions thereof.

FIG. 2 is a flow chart illustrating operations of the electronic controlunit of the present invention including the operation of the centralprocessing unit and also the operation of a central processing unittemperature control assembly.

FIG. 3 is a diagram illustrating sensor inputs and control signaloutputs and basic functions performed by an electronic control unit.

FIG. 4 is a typical engine fuel map expressed in rectangularcoordinates.

FIG. 5 is a schematic illustration of an electronic control unit for afuel injection system.

FIG. 6 is a graph of heater output as a function of CPU temperature fora typical CPU temperature control assembly of the type illustrated inFIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

A two-stroke engine unit 10 of the present invention is shownschematically in FIG. 1. In general, the two-stroke cycle engine unit 10comprises an engine assembly 12, an ignition assembly 14, a fuel/airinput assembly 16, an electronic control assembly 18 and an electricalpower supply assembly 20.

ENGINE ASSEMBLY

The engine assembly 12 illustrated in FIG. 1 is of a type which isconventional and well known in the art. The engine assembly comprises acylinder cavity 30 which is generally referred to in the art simply as acylinder. The cylinder cavity is defined by a cylindrical sidewall 32and a circular top wall 34 which is fixedly attached to the sidewall 32.The engine assembly also comprises a generally pear-shaped crankcasecavity 36 which is generally referred to in the art simply as acrankcase. The crankcase cavity is defined by a crankcase sidewall 38which is fixedly connected at the upper portion thereof to a lowerportion of cylindrical sidewall 32. The crankcase wall is fixedlyconnected at a lower portion thereof to a base plate 40. The cylindricalcavity 30 and crankcase cavity 36 thus provide the upper and lowerportions of a continuous total engine cavity. A cylindrical piston 42 isslidingly mounted in cylindrical cavity 30 and is pivotally attached toa connecting rod 44 which is, in turn, pivotally attached to a portionof crankshaft 46 which rotates, as indicated at 47, about a crankshaftcentral axis of rotation 48. The reciprocal motion of piston 42 withincylinder 30 is transferred by connecting rod 44 and crankshaft 46 to aconventional drive assembly 50 of an associated machine such as, forexample, a snowmobile 12.

A fuel/air mixture which is sometimes referred to herein as combustionfluid or combustion material is drawn into the crankcase 36 through acombustion fluid inlet 52 sometimes referred to herein as an intake port52. The intake port 52 is positioned at an upper portion of crankcase 36and is cyclically opened and closed by reciprocation of piston 42.Transfer passages 54, 56, etc., having crankshaft transfer passageopenings 58, 60, etc., and cylinder transfer port openings 62, 64, etc.,enable transfer of compressed combustion fluid within the crankcase 36to the cylinder 30. The cylinder transfer passage openings 62, 64, etc.,are cyclically opened and closed through reciprocal motion of piston 42.A cylinder exhaust gas outlet 66 sometimes referred to herein as exhaustport 66 is provided in the cylinder sidewall 32 to discharge burnedcombustion fluid from cylinder 30. Exhaust port 66 is also cyclicallyopened and closed by reciprocation of piston 42. The engine assembly maycomprise a plurality of cylinder/crankcase/piston assemblies identicalto those described above which are operably connected to commoncrankshaft 46.

The mechanical operation of the two-cycle engine assembly, in general,is as follows. During upward motion of piston 42, crankcase intake port52 is progressively opened and cylinder transfer passage openings 62, 64and cylinder exhaust port 66 ar progressively closed causing fuel/airmixture to be drawn into crankcase 3 through port 52 and causing fluidair mixture in cylinder 30 to be retained therein and progressivelycompressed. When the piston 42 reaches approximately its upward limit ofmotion or "top dead center" (T.D.C.), sparkplug 70 ignites the fuel/airmixture driving piston 42 downwardly. During the downward movement ofthe piston, cylinder exhaust port 66 is progressively opened, cylindertransfer port openings 62 and 64 are progressively opened and crankcaseinlet 52 is progressively closed causing fuel/air mixture within thecrankcase to be compressed and forced through the transfer passages 54,56 into cylinder 30. The inflow of fresh fuel/air mixture into cylinder30 is physically channeled into the cylinder in a manner to drive outburned exhaust gas within the cylinder out through exhaust port 66.During the subsequent upward movement of the piston 42, theabovedescribed cylinder fuel/air compression and crankcase fuel/airintake is again repeated, etc.

Ignition Assembly

Ignition assembly 14 comprises a conventional sparkplug mounted withincylinder 34 for igniting the fuel/air mix therein. Sparkplug 70 isconventionally connected to an ignition coil 72 which is, in turn,conventionally connected to an electrical power supply 20 andconventional timing apparatus 74 which may be conventionally linked tocrankshaft 46. In an engine assembly with a plurality ofcylinder/crankcase/piston assemblies, each cylinder is provided with aspark plug.

Fuel Air Input Assembly

Fuel air input assembly 16 includes an air manifold 80 mounted in fluidcommunication with crankshaft intake port 52. A throttle valve 82, whichin a preferred embodiment comprises a conventional butterfly valve,divides the air manifold 80 into an upstream portion 84 which is influid communication with atmospheric air 8 through conventional airfilters, etc. (not shown) and a downstream manifold portion 86 whichopens directly into crankcase 36. In the case of a multiple cylinderengine, there may be a single manifold upstream portion and a pluralityof downstream portions, one for each cylinder/crankcase. An electricallyoperated fuel injector 92 comprising a solenoid valve portion 94 and agas jet nozzle portion 96 is mounted so as to discharge a gas spray intothe downstream manifold portion 86 to produce a fuel/air mixture in thedownstream manifold portion which is subsequently drawn into crankcase36. The fuel injector may be of a convention commercially available typesuch as Bosch 280150-007 available from the Robert Bosch Company, orNAPA 217514 available from Echlin, Inc., Branfort, Conn., 06405. Thefuel injector 92 is connected at the solenoid valve end thereof to afuel circulation conduit 98 which is in fluid communication with a fuelreservoir 102 in fuel tank 100. The fuel circulation conduit comprises aconduit first end 104 connected to a fuel tank outlet 106 and a secondend 108 connected to a fuel tank return inlet 110. An electric fuel pump112 is provided for pumping fuel, such as gasoline, through the conduit98. The electric fuel pump 112 is operably connected in fluidcommunication with the conduit at a point thereon between the fuel tankoutlet 106 and the fuel injector 92. Conventional speed controlcircuitry 113 is provided to control the relative pumping speed of thefuel pump in response to a signal from the electronic control assembly18 as discussed in further detail below. The fuel pump is conventionallyconnected to the electrical power supply assembly 20 from which it drawsits operating energy. A conventional mechanically operated pressurelimiting regulator 114 is operatively mounted in the fuel circulationconduit at a point between the fuel injector 92 and the fuel tank returninlet 110. Pressure regulator 114 prevents the fluid pressure in thecirculating conduit from exceeding a predetermined maximum pressurewhich may be, e.g. 42 psia. A conventional coarse fuel filter 116 may beprovided in the circulating conduit between fuel tank outlet 106 andfuel pump 112. A conventional fine fuel filter 118 may be provided inthe circulating conduit between the fuel pump and injector 92. As shownin phantom in FIG. 1, the above-described fuel system may be employed toprovide fuel to further fuel injectors 120, 122 which are attached influid communication with the circulating conduit between the first fuelinjector 92 and the pressure regulator 114. These fuel injectors 120,122 may be mounted in manifold assemblies which may be identical tomanifold assembly 16 described above and which are in turn associatedwith ignition assemblies and cylinder/crankcase piston assemblies 121,123 which may be identical to those described above and which may beoperably connected to a common electronic control assembly 18 andelectrical power supply assembly 20.

Electronic Control Assembly

Electronic control assembly 18 includes a central processing unit 130described in further detail below which is operably connected toconventional interface circuitry 132 which may comprise conventionalanalog to digital (A/D) circuitry for converting analog sensor signalinputs to digital signal inputs and which may further compriseconventional digital to analog (D/A) interface circuitry used to convertdigital CPU command signals to analog command signals which are used tocontrol various engine operating components as described below.

The electronic control assembly comprises a number of sensors havingsensor outputs which are provided to the CPU 130 through interfacecircuitry 132. These sensors may include a battery voltage sensor 134,an air temperature sensor 136, an engine temperature sensor 138, anengine speed sensor 140, an ignition timing sensor 142, a barometricpressure sensor 144, and a throttle position sensor 146. The batteryvoltage sensor may comprise a conventional sensor or current sensingcircuit well-known in the art. The air temperature sensor 136 maycomprise a T55101 NAPA sensor mounted in the engine manifold. The enginetemperature sensor 138 is mounted on the cooling fins of an air-cooledengine or may comprise a TS 4000 NAPA mounted within the engine coolingwater jacket of a liquid cooled engine. The engine speed sensor 140 maycomprise a conventional electronic encoder mounted on the crankshaft orassociate drive linkage. In such an engine speed sensor configuration,an engine speed value is determined by counting the number of encoderpulses occurring within a fixed time interval. This timing interval maybe provided by an external clock pulse signal or a CPU internal clocksignal. The ignition timing sensor 142 may comprise an electric signalsensor connected directly to the ignition coil 72 for sensing the timeof ignition of each cylinder. In such an ignition timing sensorconfiguration, the CPU is programmed to respond to only one cylinderignition pulse per engine revolution. Thus, for example, in a threecylinder engine, the CPU would respond to only the first ignition coilpulse in each three pulse set associated with a complete enginerevolution. Similarly, the ignition timing sensor signal may be deriveddirectly from encoder signal 140 simply through counting the number ofencoder pulses which are associated with a single revolution of theengine and generating a timing pulse after the occurrence of such apredetermined number of encoder pulses.

Barometric pressure sensor 144 may be mounted in any convenient locationwhere it is exposed to the atmosphere such as, for example, on thehousing of the CPU 130. The barometric pressure sensor 144 may be any ofa number of commercially available sensors such as a Motorola MPX 201.Throttle position 146 senses the relative amount of opening of thethrottle butterfly valve 82 and may comprise a conventionalpotentiometer unit.

The CPU 130 receives and processes the signals from the various sensorsdescribed above and generates control signals which are used to controlfuel pump speed, to maintain the speed of operation of the fuel pump ata rate which provides a pressure in the circulation conduit portionimmediately downstream therefrom which is approximately equal to thepreset maximum pressure of the pressure regulator 114. The CPU 130 alsogenerates control signals which actuate the solenoid valve portion 94 ofeach fuel injector 92 to selectively open and close and injector toprovide a proper amount of fuel injection into the manifold asdetermined by the CPU. The CPU 130 may also provide a number of othercontrol functions a described in further detail below. The CPU 130, in apreferred embodiment of the invention, comprises a conventionalmicroprocessor chip 171, FIG. 5, such as a Motorola 6502 and aconventional memory chip 173, FIG. 5, which may be a PROM or EPROM chipsuch as, for example, Motorola 2532.

The electronic control assembly may also comprise a CPU temperaturecontrol assembly. One embodiment of such a temperature control system isillustrated in FIG. 5 in which CPU 130 is mounted within a relativelysmall, e.g. 10 cubic inches, CPU protective enclosure box 170 whichdefines a local CPU environmental enclosure 172. The box 170 may be 2.5inches×5 inches×0.75 inches. Also positioned within the CPU environmentenclosure are a conventional heating coil 174 having terminals 175, 177,which may have a resistance of 50 ohms, and a conventional thermistor176, which may be, e.g., an NTC 750 ohm thermistor. The heater elementand thermistor are connected as shown in an electronic circuitcontaining a second resistor 178 having terminals 183, 185 and having aresistance of 10,000 ohms, and a Darlington transistor 180 having a gateterminal 187, a collector terminal 189, and an emitter terminal 191,which may be a Motorola 6668 which may have an amplification of 400%.The circuit containing the circuit elements 174, 176, 178, 180 isconnected to the positive pole of a battery 182 and a ground (ornegative pole of a battery) 184. The battery 182 may also be used toprovide power for CPU 130. Battery 182 may be same or different from thebattery 150 used to provide energy to the engine ignition system, etc.The voltage drop across 182, 184 may be, e.g., 5 volts. Thecharacteristics of the particular circuit elements 174, 176, 178, 180may be selected to provide a heating energy response to particulartemperature conditions such as indicated in FIG. 6 for rapidly heatingthe CPU environment 172 to a predetermined maximum threshold value suchas 60° F. It will thus be seen that the heating circuit indicatedgenerally at 186 is adapted to maintain the CPU at a temperature whichis above a predetermined low temperature, e.g. 60° F., below whichcertain components of the CPU are subject to a greatly increasedprobability of malfunction. It will of course be appreciated that thispredetermined temperature may be chosen to have a value well above atemperature at which malfunction is probable. A heating circuit such asillustrated at FIG. 5 may be provided relatively inexpensively and thuseliminates the need for expensive CPU chips which are adapted to beoperable under low temperature conditions. The heating circuit such asillustrated at FIG. 5 is adapted to be particularly effective underconditions associated with the usage of snowmobiles and other winteroperated machines such as snowblowers, etc.

Electric Power Supply

The engine electric power supply 20 may comprise conventional powersupply components such as a battery 150 which may be a conventional12-volt battery and other power generating devices such as alternator orgenerator which are represented schematically at 152. Power to theelectronic control assembly 18, fuel input assembly 16, and otherelectrically-operated components may be provided through conventionalconductors 154 operably connected to a switching assembly 156 which maybe a snowmobile ignition switch, etc.

An engine unit comprising multiple cylinder/crankcase/piston assemblies12A, 12B, 12C in engine assembly 12 and comprising an ignition assemblywith multiple spark plugs 70A, 70B, 70 with a common crankshaft 146 anda common electronic control assembly 18 and a common power supply 20 isshown in FIG. 1A.

Having thus described the overall construction and operation of thetwo-stroke cycle engine unit 10 in general, certain specific features ofthe electronic control assembly 18 will now be described in greaterdetail.

Control System Functions

The basic functional steps performed by the control assembly centralprocessing unit 130 is illustrated in FIG. 2. As illustrated at 300, thecontrol system becomes operational by switching the system on. In atypical use environment such as when the control system is used inassociated with a snowmobile engine, step 300 would be performed byturning the snowmobile ignition switch to the "on" position. Asillustrated at 301 switching the system on causes electrical energy tobe provided to the CPU which initializes all ports and functions of theCPU. Next, the CPU reads the engine speed and throttle position whichare indicated as RPM and T.P., respectively, in block 302. Next, asindicated in blocks 303-307, the CPU determines whether or not theengine is to be primed. The sequence of steps 302-307 comprises whatwill be referred to herein as a "cold start circuit". As indicated at303, the CPU determines from the reading taken at 302 whether or not theengine RPM is greater than 0. If engine RPM is greater than 0, the CPUnext makes the determination from the throttle position reading of 302whether or not the throttle position is greater than a predeterminedamount, such as 20°, as indicated in block 304. If throttle position isless than 20°, the CPU decision-making process returns to block 302. Ifthe throttle position is greater than the predetermined amount andRPM=0, the CPU provides a control command to the engine fuel injector(s)to prime the engine. In a preferred embodiment of the invention, anengine priming pulse of a predetermined fixed duration associated with apredetermined fixed amount of fuel, e.g. 100 milliliters per injector,is sent to each fuel injector in response to a prime engine command fromthe CPU. After an initial engine priming function indicated at 305 hasbeen performed, the CPU again reads throttle position as indicated at306. After reading the throttle position, the CPU again determineswhether or not the throttle position is greater than a predeterminedamount such as 20°. If the throttle position is greater than 20°, thenthe CPU again returns to decision step 306 and repeats step 306, 307until the throttle position is less than 20°. In a typical operatingenvironment, this would be the equivalent of waiting for an operator torelease an opened throttle lever/pedal. Once the throttle position isreduced to below 20°, as indicated at block 307, the CPU decision-makingprocessing returns to block 302, causing the cold circuitdecision-making process of blocks 302-307 to be repeated until engineRPM is greater than 0. After engine RPM becomes greater than 0, the CPUreads all of the input values from the various sensors, as shownschematically in FIG. 3.

Next, as indicated at 309, the CPU determines a base fuel value from a"fuel map" and the engine speed input and the throttle position input. Afuel map is prepared and stored in permanent memory of the CPU basedupon the operating characteristics of the particular engine which isbeing controlled. The fuel map is prepared and stored in permanent CPUmemory in an initial production step before the CPU is used to controlthe engine. A typical fuel map is illustrated in FIG. 3 in which thehorizontal axis is indicative of engine RPM value and the vertical axis,as indicated at the right-hand side of the fuel map, is indicative ofthrottle position. Throttle position may be expressed, for example, inangular degrees of throttle opening or may be expressed in assignednumbers relating, non-linearly, to throttle opening which enables ahigher resolution of the fuel map in certain critical regions of anengine power curve. The data array shown in FIG. 3 indicates the optimumbase fuel value in milliliters for an engine fuel injector single pulseunder predetermined standard operating conditions for any given engineRPM and throttle position. For example, if the engine RPM is 6000 andthe throttle position is 25, the optimum base fuel value as indicatedfrom the fuel map is 20 milliliters under standard operating conditions.It will, of course, be appreciated that the information provided in thefuel map may be stored in various electronic forms such as in algorithmform as well as look-up table form. It will also be appreciated that theresolution of the fuel map may be provided to conform with theresolution of the RP and throttle position sensing signals and with theresolution requirements of the control system.

The base fuel value from the fuel map (FIG. 4) reading performed inblock 309 and indicated as V-1 is stored in CPU memory and is modifiedin steps 310-313 based upon the various input values read in block 308.As indicated at block 310, the base fuel value is first modified basedon the air temperature input. At a predetermined operating temperature,e.g. standard operation conditions of 70° F., no modification isperformed. If the temperature is above or below this predeterminedvalue, then the base fuel value is modified accordingly based upon apredetermined algorithm or look-up table which is stored in permanentmemory. Algorithms for engine fuel requirement modification based uponambient air temperature are well-known in the art. The modified basevalue determined based upon air temperature modification is indicated asV-2.

As indicated in block 311, the modified base value V-2 is next furthermodified based upon the barometric pressure reading. This modificationmay again be performed by use of a conventional algorithm or look-uptable stored in permanent memory. The resulting modified fuel value isindicated as V-3.

As indicated in block 312, modified value V-3 is next further modifiedbased upon engine temperature. The modified value is indicated as V-4.This modification may be made either from a stored algorithm or a storedlook-up table which is prepared based upon the particular enginetemperature operating characteristics of the subject engine.

Next, as indicated in block 313, the modified fuel value V-4, which isindicative of the total corrected (compensated) fuel amount that eachinjector should inject into the engine during each revolution thereoffor optimum performance, is used to determine the duration of injectoropening which is required to provide fuel injection in the amount of V-4under predetermined fuel injector parameters, e.g. with a known,constant fixed fuel pressure and a known, fixed injector orifice size,etc. This duration is indicated at V-5 and may be expressed inmilliseconds. An alternative to modifying base fuel value is sequentialsteps as described above in 310-312; relative correction factors may besimultaneously computed based on the variables indicated in 310-312 anda total correction factor may be derived therefrom and applied to thebase fuel value to arrive at a total corrected fuel amount V-4.

Next, as illustrated in blocks 314 and 315, the CPU determines whether apredetermined cyclically reoccurring state (repeating once per enginerevolution) of the engine, such as, for example, a top dead centerposition of a selected one of the pistons, has been reached. Once thatcyclically reoccurring engine state has been reached, the CPU provides acontrol command to the fuel injector(s) causing the fuel injector(s) tobe opened for the predetermined length of time V-5 calculated in step313. It will be appreciated that for a multiple cylinder engine theinjectors may be opened sequentially at a predetermined spacing in timeassociated with the piston positions in the various cylinders, or all ofthe injectors may be opened simultaneously. In the preferred embodimentof the invention, all of the injectors are opened simultaneously due tothe fact that, with the injection of fuel into the manifold, as opposedto conventional fuel injection into the crankcase, the sequential timingof injectors in unnecessary.

Next, as indicated in block 317, the engine RPM value from step 308 iscompared to a predetermined maximum desired engine RPM such as, forexample, 8500 RPM. If the engine speed is less than the predeterminedmaximum value, then the CPU again returns to operating step 308 andrepeats steps 308-317. If the engine speed is greater than thepredetermined value, then, as indicated in block 318, the CPU provides acontrol signal which closes the fuel injectors.

Next, as indicated in block 319, the CPU again reads the RPM inputvalue. If the RPM input value is greater than a predetermined valuewhich may be less than the maximum engine RPM (e.g. 8200 RPM), then thefuel injectors are retained in a closed positioned as indicated in step318, and steps 319 and 320 are repeated. If the engine speed is lessthan 8200 RPM, then the CPU returns to step 308. Thus, once the enginereaches 8500 RPM, the fuel injectors are closed and remain closed untilengine speed drops to 8200 RPM. This total termination of fuel asopposed to conventional speed control methods which simply reduce fuelinjection amount or terminate ignition prevents damage to the engine orspark plug fouling associated with such prior art methods.

It will be understood by those with skill in the art that the totalcorrected (compensated) fuel value may be based on an average derivedfrom several iterations of sensor inputs and total corrected fuel valuecalculations. It will also be appreciated that the actual fueladjustments may be made at intervals less frequent than those in whichtotal fuel value calculations are made, e.g. input readings and fuelvalue calculations may be made 100 times per second and total fuelinjection duration may be adjusted 16 times per second.

The CPU 130 may also control pump speed based upon engine RPM. Forexample, at engine start up when RPM=0, the fuel pump may be actuated bya control signal from CPU 130 to cause it to run at full speed for onesecond and then stop until RPM is greater than zero. Above RPM=0, theCPU may cause the pump to run at 50% of its rated capacity (drawingone-half its normal maximum current amount) up to a predetermined enginespeed, e.g. 3600 RPM. Above this predetermined speed, the CPU may causethe pump to operate at 100% of its rated capacity. Of course, more thantwo pumping rates may be provided, if desired, based upon a plurality ofdifferent engine RPM ranges. Such an arrangement, as well as providingoptimum pressure, reduces energy draw on the electrical power supply atstart-up and at low RPM.

As further indicated by FIG. 2, the switching on of the ignition, etc.,at step 300 also operates a control circuit which functionsindependently from the CPU 130 which performs the functions indicated insteps 300-320. In this independent circuit, as indicated at step 330,the temperature in the immediate environment of the chip components(e.g. microprocessor, EPROM, etc.) which comprise CPU 130 is initiallydetermined. Next, as indicated at step 331, if the temperature withinthe CPU environment is greater than a predetermined temperature, suchas, for example, 60° F., then the system returns to step 330 and cyclesbetween 330 and step 331. When the temperature in the immediateoperating environment of the CPU is sensed to be below the predeterminedtemperature, then the system actuates a temperature control device, suchas a heating coil, to elevate the temperature in the environment of theCPU. Next, as indicated at step 333, the temperature within theoperating environment is again read and compared to a predeterminedtemperature which may be the same or higher than the minimum temperatureof step 331. If the temperature is below this second predeterminedtemperature, such as, e.g. 60° F., then the temperature control devicecontinues to operate. If the temperature exceeds this secondpredetermined temperature, then the operation of the temperature controldevice is terminated and the system again returns to step 330.

It will be appreciated that these general control functions described insteps 330-335 apply to any system which is designed to maintain thetemperature within a particular environment within a predeterminedtemperature range. Such temperature control could be performed by anynumber of conventional heating/air conditioning systems. In thepresently preferred embodiment, a temperature control system which isnot subject to malfunction at lowered temperatures, e.g -b 60° F., isprovided such as illustrated in FIG. 5 and discussed above.

All "Motorola" components indicated herein are commercially availablefrom Motorola, Inc., 8201 E. McDowell Road, Scottsdale, Ariz.,85257-3812. All "NAPA" components indicated herein are commerciallyavailable from Echlin, Inc., Branfort, Conn., 06405.

While an illustrative and presently preferred embodiment of theinvention has been described in detail herein, it is to be understoodthat the inventive concepts may be otherwise variously embodied andemployed and that the appended claims are intended to be construed toinclude such variations except insofar as limited by the prior art.

What is claimed is:
 1. A fuel injection system for a two-stroke cycleengine of the type comprising at least one cylinder, a crankcaseassociated with said cylinder, a piston reciprocally mounted in saidcylinder and crankcase; a reciprocally openable and closable crankcaseinlet for enabling combustible fluid to be drawn into the crankcase, areciprocally openable and closable transfer port for transferringcombustible fluid compressed in said crankcase to said cylinder, anignition system for igniting compressed combustible fluid in saidcylinder, a reciprocally openable and closable exhaust port in saidcylinder for enabling exhaust of burned combustible fluid from saidcylinder, a crankshaft connected to said piston for transferringmechanical energy from said piston to a drive unit, and an electricalenergy supply source including a battery for operating the ignitionsystem and other electrical components, comprising:(a) fuel injectionmeans for injecting fuel for combustion within said cylinder; (b) fuelsupply means for supplying fuel to said fuel injection means; (c)battery voltage sensing means for sensing battery voltage and forproviding a battery voltage sensing signal representative thereof; (d)air temperature sensing means for sensing the temperature of ambient airand for providing an air temperature signal representative thereof; (e)engine speed sensing means for sensing the speed of revolution of saidengine and for providing an engine speed signal representative thereof;(f) timing sensing means for sensing each occurrence of a predeterminedcyclically repeating state of said engine and for providing a timingsignal indicative thereof; (g) barometric pressure sensing means forsensing atmospheric air pressure and for generating a barometricpressure sensing signal representative thereof; (h) throttle positionsensing means for sensing the relative amount of opening of saidthrottle valve means and for generating a throttle position signalrepresentative thereof; (i) first data processing means for receivingand processing said sensing signals comprising:(i) means for processingsaid engine speed sensing signal and said throttle position sensingsignal and for generating a priming control signal to said fuelinjection means for selectively injecting or not injecting fuel intosaid manifold means based on said engine speed signal and said throttleposition signal; (ii) means for receiving and processing said enginespeed signal and throttle position signal for determining a base fuelinjection value; (iii) means for receiving and processing said airtemperature signal and calculating an air temperature modification valueof said base fuel injection value; (iv) means for receiving andprocessing said barometric pressure sensing signal for calculating abarometric pressure modification value of said base fuel injectionvalue; (v) means for receiving and processing said engine temperaturesignal for calculating an engine temperature modification value of saidbase fuel injection value; (vi) means for determining a total fuelinjection value representative of the total fuel amount which is to beinjected by said fuel injection means during a single two-strokeoperating cycle of said piston from said base fuel injection value, saidair temperature modification value, said barometric pressuremodification value, and said engine temperature modification value;(vii) means for determining an injector open duration interval based onsaid total fuel injection value and a known fuel output rate capacity ofsaid fuel injection means; (viii) means for generating a control signalfor opening said injection means for said determined injector durationopen interval at a predetermined point in time determined from saidtiming sensing signal; (ix) means for receiving and processing saidengine speed sensing signal for generating a pump control signal inresponse thereto for maintaining said pump at an optimum operating speedfor providing said predetermined maximum operating pressure in said fuelcirculation conduit means at said pump.